The present invention relates in general to methods and products for initiating an immune response against an antigen, and in particular relates to transepithelial delivery of antigens to provoke tolerance and immunity.
The present invention further relates to methods and products for the transepithelial delivery of therapeutics. In particular, the invention relates to methods and compositions for the delivery of therapeutics conjugated to a FcRn binding partner to intestinal epithelium, mucosal epithelium and epithelium of the lung. The present invention further relates to the synthesis, preparation and use of the FcRn binding partner conjugates as, or in, pharmaceutical compositions for oral systemic delivery of drugs and vaccines.
The immune system of a mammal develops during gestation and becomes active in the late mammalian fetus. Although active, it still might be characterized as xe2x80x98immaturexe2x80x99 because it has not been challenged to any significant extent by antigens; the fetus is largely protected from antigens by the mother. This xe2x80x98immaturexe2x80x99 immune system, however, is supplemented by the transfer of maternal immunoglobulin to the fetus (or in some cases to the neonate) to provide humoral immunity during the first weeks of independent life.
Rats and mice receive most maternal immunoglobulin G (IgG) by suckling from colostrum and milk, although some is acquired prenatally. Cattle also receive IgG from colostrum. In rabbits, IgG is transported to the fetus across the yolk sac. Little is known about the transfer of IgG to the fetus or neonate in humans. Most evidence suggests that human mothers transfer humoral immunity to an offspring only before birth, although IgA transferred to a neonate via breast milk is believed to play a role in protecting the neonate against enteric infection.
The delivery of maternal IgG to the mammalian fetus and/or neonate requires transport across an epithelial barrier which is largely impervious to macromolecules. The transport of macromolecules across such an epithelial barrier may occur by non-specific and specific receptor-mediated mechanisms. Receptor non-specific mechanisms are represented by paracellular sieving events, the efficiency of which are inversely related to the molecular weight of the transported molecule. Transport of macromolecules such as IgG across this paracellular pathway is highly inefficient. Descriptions of receptor-mediated transport of immunoglobulins through intestinal epithelial cells are limited thus far to the polymeric immunoglobulin receptor and the enterocyte receptor of IgG (a major histocompatibility complex (MHC) class I related Fc receptor). These two receptor systems differ in their specificity for immunoglobulin isotype, in their direction of immunoglobulin transport across the epithelial cell and in their tissue-specific expression. Both may play a role in molding the immature immune system.
The polymeric immunoglobulin receptor is expressed on the basolateral surfaces of enterocytes, hepatocytes and/or biliary duct epithelial cells. It transports polymeric IgA and IgM to the apical (luminal) surfaces, concentrating these immunoglobulins for antimicrobial defense and antigen exclusion.
The enterocyte receptor for IgG, which has homology to the MHC class I heavy chain and is associated with beta2-microglobulin (xcex22M), is expressed on neonatal enterocytes of the rat and mouse. IgG is transported transcellularly in a luminal to serosal direction across the intestinal epithelium of these rodent neonates. On the apical surface of the enterocyte, the Fc portion of IgG is bound to the enterocyte receptor at the relatively acidic pH of the lumen (about pH 6.0). Following transcytosis to the basolateral plasma membrane, discharge of the immunoglobulin occurs at the relatively neutral pH of the interstitial fluids (about pH 7.4). The rodent neonatal Fc receptor (FcRn) therefore could be responsible for delivery of maternal IgG to the neonate and as such may be responsible for the passive acquisition of IgG during this period.
In humans, maternal IgG is actively transported across the placenta. The receptor responsible for this transport has been sought for many years. Several IgG-binding proteins have been isolated from placenta. Fcxcex3RII was detected in placental endothelium and Fcxcex3RIII in syncytiotrophoblasts. Both of these receptors, however, showed a relatively low affinity for monomeric IgG. Recently, the isolation from placenta of a cDNA encoding a human homolog of the rat and mouse enterocyte receptor for IgG was reported. (Story, C. M. et al., J. Exp. Med., Vol. 180:2377-2381, December 1994) The complete nucleotide and deduced amino acid sequence is reported. This Fc receptor for IgG may be responsible for the transport of maternal IgG to the human fetus (and even possibly to the neonate), as the molecule is highly homologous over its open reading frame with the rat FcRn sequence (69% nucleotide identity and 65% predicted amino acid identity). So called passive immunization in the human fetus (and possibly in the human neonate) now may become better understood.
In contrast to passive immunization which involves supplementing a host""s immune system with antibodies derived from another, active immunization involves stimulation of the host""s own immune system to generate in vivo the desired immune response. The most widely practiced methods of active immunization in children and adults involve injections of an immunogen, once as an initial dose and then at least once again as a booster dose. These methods suffer many serious drawbacks, including the risks associated with the use of needles that can transmit diseases such as AIDS and hepatitis. (When tolerizing a patient against an allergen, the problems are compounded in that repeated injections over a long period of time often are required.) These methods also do not necessarily trigger adequately the first line of defense against many pathogens, that is, mucosal immunity. Mucous membranes line the airways, the reproductive system and the gastrointestinal tract, and this mucosal surface represents the first portal of entry for many diseases. An oral vaccine that is easy to deliver and that triggers mucosal immunity would be highly desirable.
Immunization using oral vaccines is problematic. Often little or no immune response is achieved. To enhance the immune response, antigens of interest have been coupled to carriers that are known to be strongly immunogenic. For example, researchers have delivered antigens using Bacille Calmette-Gurein (BCG) as a carrier; BCG is a bacterium originally used as an oral vaccine against tuberculosis. A problem with such carriers is that the patient will develop antibodies against the carrier itself, which can be troublesome if the carrier is used again for delivering a different antigen to the same patient. To date, no general strategy for oral vaccine: has proven successful.
Immunoglobulin and portions thereof in the past have been conjugated to drugs and imaging agents to target and destroy cell populations and to extend the half-lives of certain agents. Immunotoxins are an example of such conjugates. Such conjugates, however, have never been proposed as useful for initiating an immune response.
A small body of work has focused on the tolerogenic capacity of immunoglobulins coupled to oligonucleotides or proteins characteristic of autoimmune diseases. (See PCT WO 91/08773). This work is based upon the notion that the induction of tolerance may be strongly influenced by carrier moieties and that immunoglobulin carriers appear to be strongly tolerogenic. Isologous IgG is the preferred carrier, and intravenous administration was the mode used for delivering the conjugates of IgG. Although this body of work extends for more than a decade, oral administration is mentioned only once and only for conjugates where IgA is the immunoglobulin carrier. Thus, although tolerogenic immunoglobulin conjugates are known in the art, such conjugates have never been suggested as agents for inducing a robust response against an antigen characteristic of a pathogen. (To the contrary, the art suggests that such conjugates, if anything, would tolerize a subject against a pathogen which would be highly undesirable). In addition, it never has been suggested that such conjugates would be effective tolerogens when the immunoglobulin is IgG and the mode of delivery is oral delivery.
The invention involves the discovery that antigens may be coupled to molecules that bind to the FcRn receptor, such as immunoglobulins, or portions thereof, and delivered across epithelial barriers by active transport through the enterocyte via FcRn receptors. The immunoglobulin or portion thereof binds to the FcRn receptor and acts as a carrier for the antigen as the immunoglobulin or portion thereof is transported across the epithelial barrier by FcRn mediated-transport. The FcRn receptor is present in the human epithelial tissue of children and adults, and the invention therefore permits effective strategies for immunizing humans.
According to one aspect of the invention, a method for modulating the immune system of a mammal is provided. An effective amount of a conjugate of an antigen and a FcRn binding partner is administered to an epithelial barrier of a mammal in need of such immune modulation. The antigen is selected from the group consisting of: an antigen that is characteristic of a pathogen, an antigen that is characteristic of an autoimmune disease, an antigen that is characteristic of an allergen and an antigen that is characteristic of a tumor.
The FcRn binding partners of the present invention may be utilized for the delivery of a wide variety of compounds and therapeutics and bioactive substances, including but not limited to, chemotherapy agents for the treatment of cancer, cytokines, including interferon; and hormones including insulin, human growth hormone (HGH), fertility drugs, calcitonin, calcitriol and other bioactive steroids. The FcRn binding partners of the present invention may further be utilized for the targeted delivery of a delivery vehicle, such as liposomes.
In preferred embodiments, the FcRn binding partner is non-specific IgG or a FcRn binding fragment of IgG. Most preferably the FcRn binding partner is an Fc fragment of IgG. It also is preferred that the antigen be covalently coupled to the FcRn binding partner. Preferably the conjugate is administered orally to the intestinal epithelium, in an aerosol to the lungs or intranasally. Such preparations may be nonaseptic. Supplementary potentiating agents, as described below, may be administered in addition.
In a preferred embodiment, when the compound to be delivered is a peptide or protein, the FcRn binding partner protein conjugate may be synthesized as a recombinant fusion protein. Examples of peptides and proteins which may be conjugated in this manner include cytokines; chemokines; growth factors, insulin, erythropoietin (EPO), neuropeptides, neuropeptide Y, neurotensin, transforming growth factor xcex1, transforming growth factor xcex2, interferon (IFN), and hormones.
The pharmaceutical compositions of the present invention relate to FcRn binding partners conjugated to bioactive substances, including vaccines or drugs for oral, sublingual or intranasal systemic delivery. The pharmaceutical preparation of the present invention includes a conjugate of an antigen and a FcRn binding partner, wherein the antigen is selected from the group consisting of: an antigen that is characteristic of a pathogen, an antigen that is characteristic of an autoimmune disease, an antigen that is characteristic of an allergen and an antigen that is characteristic of a tumor. The pharmaceutical preparation of the present invention includes a conjugate of a drug or therapeutic and a FcRn binding partner. The preferred-FcRn binding partners are as described above. The conjugate is present in an amount effective for modulating the immune response of a mammal. The pharmaceutical preparation of the present invention also includes a pharmaceutically acceptable carrier. When the antigen is characteristic of an autoimmune disease or an allergen, then the pharmaceutical preparations of the invention must be formulated in unit dosage form constructed and arranged for delivery to an epithelial carrier such as for oral delivery to the intestinal epithelium, aerosol delivery to the pulmonary epithelium and intranasal delivery to the nasal epithelium. Thus tablets containing IgG (or an FcRn binding portion thereof) coupled to any of the antigens as characterized above are embraced by the present invention.
The foregoing pharmaceutical preparations may be delivered together with supplementary potentiating agents including adjuvants, cytokines, bioadhesives and the like. The supplementary potentiating agents themselves may be coupled to a FcRn binding partner to facilitate the delivery of such agents across the epithelial barrier. Preferred modes of administration in general include oral dosages to the intestinal epithelium, aerosols to the lungs and intranasal dosages.
The present invention further relates to the synthesis, preparation and use of the FcRn binding partner conjugates of the present invention as, or in, pharmaceutical compositions for oral and intranasal systemic delivery of drugs and vaccines. The synthesis of the FcRn binding partner conjugates of the present invention comprises covalently coupling an antigen or a supplementary potentiating agent to an FcRn binding partner, wherein the antigen or supplementary potentiating agent is selected as described above. The synthesis of the FcRn binding partner conjugates of the present invention alternatively comprises covalently coupling a FcRn binding partner to a therapeutic or drug. Further, the synthesis of the FcRn binding partner conjugates of the present invention comprise covalently coupling a FcRn binding partner to a delivery vehicle, e.g. liposomes. The preferred FcRn binding partner also is as described above. The conjugates then can be used to prepare the pharmaceutical preparations of the present invention.
In yet another aspect of the invention, the conjugate including the antigen crosses the epithelial barrier in an amount at least double the extent that the antigen crosses the epithelial barrier in an unconjugated form. It thus is an object of the invention to develop a mechanism for increasing the ability of an antigen to cross an epithelial barrier.
Another object of the invention is to develop a new class of orally active immunogens and toleragens.
Another object of the invention is to develop improved methods for stimulating mucosal immunity.
These and other aspects of the invention are described in greater detail below.